Mason Plumlee looks out over the floor at Duke University’s practice facility.

It must be weird to be back—returning to campus, his home for the last four years; visiting Cameron Indoor, Duke’s 2010 national championship banner hanging in the rafters of this gymnasium that feels more like a cathedral, with its wooden steeple doors and castle-stone exterior; and sitting here in Duke’s practice facility where his new team, the Brooklyn Nets, are having training camp…